One of image forming methods which can form an image having a high image quality comparable to the image quality of color pictures using a photograph development technique is a dye thermal transfer method (see, for example, Japanese Laid-Open Publication No. 2002-86776). The dye thermal transfer method is increasingly drawing attentions as digital cameras come into wide use since an image can conveniently formed based on digital image signals imaged by digital cameras.
In the dye thermal transfer method, a dyeing layer, for example, a resin having a high pigment dyeing property on a base material, and dyes such as yellow, magenta, and cyan are sequentially pressed on and dyes the dyeing layer. The dyeing layer dyed with dyes of respective colors to transferred to a surface of a recording paper, which is plain paper, by thermal transfer. Thus, a full-color image formed on the dyeing layer is formed on the recording paper.
In image forming apparatuses employing the dye thermal transfer method, a belt body, which is a band of a polyimide film is usually used. Two ends of belt body are connected to each other so as to obtain a recording intermediate belt which does not have an end. The recording intermediate belt loops around a platen drum having a cylindrical shape which is formed to be rotatable. Thus, the recording intermediate belt revolves at a predetermined rate as the platen drum rotates.
On an outer peripheral surface side of the platen drum, a dyeing layer formation section for forming a dyeing layer on an outer surface of the recording intermediate belt, a first image formation section for dyeing the dyeing layer with a dye of yellow color, a second image formation section for dyeing the dyeing layer with a dye of magenta color, and the third image formation section for dyeing the dyeing layer with a dye of cyan color are located in this order from an upper stream side of revolving of the recording intermediate belt. On the outer surface of the recording intermediate belt which revolves along the outer peripheral surface of the platen drum, first, a dyeing layer is formed at the dyeing layer formation section. Then, the dyeing layer is dyed with dyes of yellow, magenta, and cyan, respectively, at the first image formation section through the third image formation section. The first through third image formation sections include recording heads for dyeing respective dyes by pressing. The recording heads dyes the dyeing layer with respective dyes based on an image signal. As a result, a full-color image is formed on the dyeing layer.
The full-color image formed on the dyeing layer of the recording intermediate belt is transferred to the recording paper, which is plain paper, with the dyeing layer by thermocompression bonding to the recording paper pulled out from a recording paper roll wound into a roll, for example. Thereafter, the recording intermediate belt and the recording paper bonded via the dyeing layer are guided in different direction to separate the recording intermediate belt and the recording paper. The recording paper separated from the recording intermediate belt is out into pieces of pre-determined size by a cutter and ejected out of the image forming apparatus.
In image forming apparatuses employing such a dye thermal transfer method, images are formed by sequentially performing the steps of forming a dyeing layer, dyeing with a dye of yellow color, dyeing with a dye of magenta color, and dyeing with a dye of cyan color while a recording intermediate belt looping around a platen drum revolves. Thus, images can be formed at a plurality of positions on the recording intermediate belt revolving around the platen drum at the same time. Thus, a time for forming images can be reduced when pieces of recording paper with images formed thereon are produced, thereby increasing the speed of image formation.
In the above-described dye thermal transfer method, the recording heads respectively provided in the first through third image formation sections press the recording intermediate belt for dyeing with dyes of the respective colors. Thus, images are formed. However, in the image forming apparatuses employing this dye thermal transfer method, there is a problem that, when the recording heads do not press the dyeing layer on the recording intermediate belt at the correct locations with correct pressing strength, distortion of images such as stripe lines on images occur, and definition of the images tend to deteriorate. Further, such distortions in the images may also be generated by load changes when the step of cutting the recording paper with the dyeing layer transferred thereto into pieces of a predetermined size by a cutter after it is removed from the recording intermediate belt is performed.
If image quality is deteriorated due to such image distortions, a plurality of images cannot be formed at the same time, and thus, the efficiency of image formation cannot be promoted.
Therefore, it is important to previously avoid factors which may deteriorate the definition of the images in order to stably form the high-definition images using the above-described image forming apparatuses.
Further, in the above-describe image forming apparatuses, if the size of images to be formed increases, a long time is required as image process operation time for generating a control signal for forming images. Due to the image process operation time, a blank image may be formed since the control signal cannot be in time to start image formation. Thus, the efficiency of image formation cannot be promoted.
The present invention is provided in view of such circumstances, and the object thereof is to provide an image forming apparatus and image forming method in which factors which may deteriorate the definition of images are previously avoided, and which can stably form images of a high definition and promote efficiency of image formation.